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Smart water heaters

As the world shifts towards renewable energy sources, energy storage solutions have become increasingly important. One of the most promising solutions is heat storage, which can store excess energy from renewable sources and release it when needed. Heat storage will then reduce peak demand on the electric grid, making it an attractive option for utilities and homeowners alike. Smart water cylinders and heat batteries cylinders like the ones manufactured by Mixergy and Sunamp offer an innovative way to store heat and provide hot water on demand. 

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Smart water cylinder


Heat battery for hot water

Mixergy is a smart water cylinder that uses an advanced management system to control the water temperature and reduce energy consumption. Most immersion heaters heat water from the bottom; hot water rises and mixes with cold water. The result is that you either heat the whole tank or nothing. Mixergy heats water from the top down, which means it can heat only the amount of water it expects to use. Heating less water also speeds the process: up to ten times faster than other hot water cylinders. Mixergy's intelligent management technology ensures that the cylinder is only heated when needed, further reducing energy consumption and costs. According to Mixergy, the system can save up to 40% on energy bills compared to traditional systems! Mixergy uses an innovative insulation system that minimizes heat loss, reducing energy consumption and costs. 

The smart control ensures that Mixergy charges at night when electricity is cheap and abundant. In doing so, it helps stabilise the electric grid and saves money.

Finally, Mixergy has a series of slim products which allows to fit their cylinders in standard cupboards.



Sunamp uses a phase-change material that stores heat more efficiently than water, reducing energy consumption and costs. The system is designed to work seamlessly with existing heating systems, making it easy to install and use. Sunamp's thermal energy storage system also has a smaller footprint than traditional water cylinders, making it ideal for homes with limited space. According to Sunamp, the system can save up to 75% on energy bills compared to traditional systems.

Unlike Mixergy, Sunamp does not have smart software to combine use patterns and electricity prices for the best efficiency. The recharge rate is not as fast as Mixergy. 

Sunamp batteries are on average more expensive than Mixergy tanks. 

Both Mixergy and Sunamp offer significant environmental benefits. By reducing energy consumption, they can help reduce carbon emissions and contribute to a more sustainable future. Smart water cylinders also offer greater control over water temperature, ensuring that hot water is always available when needed. According to the Energy Saving Trust, replacing a traditional water cylinder with a smart cylinder can save up to 50kg of CO2 per year.

Approximate cost of a 150L cylinder: £1250 inc. VAT

Approximate cost of a 150L battery: £2000 inc. VAT

nomoregas unagru architecture urbanism gas boilers alternative climate change energy crisis

Mixergy tank (Source: ecobubl)

nomoregas unagru architecture urbanism gas boilers alternative climate change energy crisis

Heat batteries and Sunamp (Source: Delta-EE)


1. Sunamp are about 2 times more expensive (about £ 2,000 for an equivalent energy storage to a £ 1,000 180L Mixergy tank).

2. Sunamp don't actually store more energy than a well strategies hot water tank per unit volume (if you allow the Mixergy tank to go up to 65 degree Celsius and they could push this as high as 80 degree Celsius with different ancillary components).

3. Sunamp is heavier, and don't appear to have any connectivity, intelligent control or grid measurement. They do have the advantage of a square form factor. If this proved to be popular we would recommend to use a tank of water glycol at 80 degree Celsius, plate heat exchangers and plenty of insulation.

First hand experience

We specified a Mixergy cylinder in our Westminster flat refurbishment project. To reduce space constraints, we chose the 210-litre slim mode, costing approximately £1700 inc. VAT. We spoke to several installers who were enthusiastic about the product.  

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